ABSTRACT

Studies of the coastal element of eastern North America indicate that large structural anomalies have been influenced, or even controlled, by Paleozoic and older structures. Initially, in late Permian to Jurassic times, downfaulting or downflexing of the continental margins, back of and generally parallel to the Paleozoic orogenic belts, effected unstable areas where sediments of geosynclinal proportions accumulated in the Mesozoic and Cenozoic. In the United States, certain negative areas, for example, Rio Grande syncline, oppose salients in the Appalachian and Ouachita orogenic belts. Some positive areas, as Cape Fear arch, border recesses in the belts. Others appear to be related to roughly parallel orogenic belts or to cut across Paleozoic trends. Similar, but opposite relationships, exist between Sierra Madre Oriental folds and larger structures of the coastal element in Mexico. It is suggested that they were positioned by salients and recesses in the now mostly covered Paleozoic orogenic belt and that larger, modern, structural anomalies may be used to interpret, in a very general way, the patterns of the Paleozoic structures. Offsets in Paleozoic belts and alignments of geologic features, as at south end of Coahuila peninsula, and along Champlain-Hudson valleys, suggest basement fracturing which controlled subsequent structures.